Sanjay Gupta is apologizing for "misleading" the American public on weed.

CNN's chief medical correspondent, whose documentary Weed airs on CNN this Sunday, said he had mistakenly believed the Drug Enforcement Agency had sound scientific proof when it placed marijuana in the category of the most dangerous drugs.

"I have apologized for some of the earlier reporting because I think, you know, we've been terribly and systematically misled in this country for some time," Gupta told Piers Morgan on CNN Wednesday night. "And I did part of that misleading."

Gupta has spoken out against the use of medical marijuana in the past, including penning a TIME magazine article in 2009 titled, Why I Would Vote No on Pot.

In an op-ed that appeared on CNN's website Thursday, Why I Changed My Mind on Weed, Gupta said he had been wrong about the effects of the drug.

"I apologize because I didn't look hard enough, until now. I didn't look far enough. I didn't review papers from smaller labs in other countries doing some remarkable research, and I was too dismissive of the loud chorus of legitimate patients whose symptoms improved on cannabis.

Instead, I lumped them with the high-visibility malingerers, just looking to get high. I mistakenly believed the Drug Enforcement Agency listed marijuana as a schedule 1 substance because of sound scientific proof. Surely, they must have quality reasoning as to why marijuana is in the category of the most dangerous drugs that have 'no accepted medicinal use and a high potential for abuse.' "

Gupta says he hopes his upcoming documentary will help set the record straight on medical marijuana.